We have a situation like the following image:
The only difference is the wire on the far right switch going from the switch up to the light is red instead of black.
All of those switches are powered and control each other but don't control an actual light. My thought is one of the two main living lights may previously had been a fan or something that are no longer there.
The switch in the far right of the image we want to put an insteon scene switch. The top left button would be the on and off for the switch which wouldn't actually control anything, but the 7 other buttons we could program to control scenes in the house.
We want to remove the other 2 switches that are part of the 4 way. If we just cap them all off, then the one on the far right won't be powered up and wouldn't work.
To note, the two we want to remove are each part of gang boxes with other switches so the cables would still be fully accessible later on by taking the switch face plate off for future owners.
So what we did was the middle switch in the image, attached red to red and black to black. That works. For the other switch (far left in image), not sure what we need to do, cap the all off? Attached certain wires to each other?